Merge pull request #1952 from fastrde/fixNoShiftClickAfterDrag

fixes shift clicking Issue described in (Issue #1950)
add attribution and update function
more consistent method name for ImageOverlay update
remove tailing spaces for jake build
Merge pull request #1958 from stsydow/master

Add attribution and update function to ImageOverlay [for master]
Merge branch 'zoomboxOnClickFix' of https://github.com/fastrde/Leaflet

* 'zoomboxOnClickFix' of https://github.com/fastrde/Leaflet:
  Fix for zoomBox fires map click Event (Issue #1884)
some tweaks to #1951
Merge remote-tracking branch 'upstream/master'